Patients who have experienced spinal cord trauma often face a poor prognosis for full recovery. Although minor spinal cord trauma may allow a patient full return of limb function spontaneously after cord concussion, in many cases patients retain some limb function immediately after injury only to lose this function irretrievably after a few hours.
A popular theory explaining this phenomenon is that impact injury results in spinal cord swelling which may progressively enlarge the cord so that it fills the subdural and subarachnoid spaces and produces ischemic cord transection due to vascular compromise. Earlier treatment techniques, such as surgical decompression, were developed according to this theory. More recently, others have theorized that spinal cord edema following trauma causes tissue hypoxia because of impaired oxygen diffusion or compromised circulation. Some have theorized that structural alterations and possibly other factors may be more important than edema in causing the progressive neurological deterioration which sometimes accompanies spinal cord trauma. C. Romero-Sierra et al., A New Method for Localized Spinal Cord Cooling, Medical and Biological Engineering 188 (March 1974).
Whatever the explanation for this progressive limb function loss after spinal cord trauma, it is generally known that hypothermia reduces ischemic damage to nervous tissue. Although generalized hypothermia can induce cardiac arrest, some investigators have selectively cooled portions of the spinal cord in localized areas with success. Not only has such localized hypothermia been cited as decreasing edema and improving blood perfusion in the traumatized area, but it also is believed to decrease metabolic demands of the cooled tissue.
Previous investigation shows an improvement in recovery of experimental animals whose spinal cord impact injuries are treated with induced, local hypothermia. Such procedures have also been used on human patients with apparently promising results. R. Hansebout, Current Status of Spinal Cord Cooling in the Treatment of Acute Spinal Cord Injury, 9 Spine 5:508-11 (1984). It is generally agreed, however, that induced hypothermia should be initiated within at least four hours of injury, and that the earlier the cooling is started, the better the prognosis. Id., M. Albin et al., Localized Spinal Cord Hypothermia--Anesthetic Effects and Application to Spinal Cord Injury, 46 Anesthesiology & Analgesia 8 (1967); M. Albin, et al., Study of Functional Recovery Produced by Delayed Localized Cooling After Spinal Cord Injury in Primates, 29 Journal of Neurosurgery 113 (1968); B. Green et al., Local Hypothermia as Treatment of Experimentally Induced Spinal Card Contusion: Quantitative Analysis of Beneficial Effect, 24 Surgery Forum 436 (1973).
Investigators using 5.degree. C. (41.degree. F.) baths have recorded low cord temperatures of 6.7.degree. C. (44.degree. F.) in monkeys and a 5.4.degree.-23.5.degree. C. (42.degree.-74.degree. F.) gradient in dogs, so that subfreezing temperatures are not required for effective treatment. P. Black, Spinal Cord Injury in the Monkey: Rate of Cord Cooling and Temperature Gradient During Local Hypothermia, 5 Neurosurgery 583 (1979); D. Yashon, Edema of the Spinal Cord Following Experimental Impact Trauma, 38 Journal of Neurosurgery 693 (1973).
Experiments have also established that cooling tends to be localized, coextensive with the heat exchanger and very rapid (2-3 minutes) with extradural heat exchangers. Additionally, no significant lowering of body temperature or systemic blood pressure was encountered. C. Romero-Sierra et al., A New Method for Localized Spinal Cord Cooling, Medical and Biological Engineering 188 (March 1974).
Orthopedic cervical immobilization devices are currently used to extricate accident victims who experience cervical trauma and to immobilize patients' neck areas after spinal injury. U.S. Pat. No. 4,205,667 issued June 3, 1980 to Gaylord, Jr. discloses such a collar, for instance. That patent is incorporated herein by reference. The Gaylord collar comprises a pair of U-shaped body members made of air permeable foam that are sufficiently firm to provide adequate support for the wearer's head and neck. The body members are held together in a face-to-face mating arrangement with hook and loop straps.
A more widely-used collar, the Philadelphia collar, is the subject matter of U.S. Pat. No. 3,756,226 issued Sept. 4, 1973 to Calabrese et al., which is incorporated herein by reference. The Calabrese collar has two halves formed of a soft flexible polymeric material. A rigid chin support is attached to the front half while a posterior support member extends along the spine from the back of the basal portion of the skull on the other half. The halves are held together by hook and loop fabric.
Such collars may quickly be applied to a patient's neck in an effort to immobilize the cervical cord and they are typically deployed aboard emergency medical vehicles for this purpose. They do not, however, allow the doctor or medical technician to treat the cervical cord injury at the accident scene or during extrication by heating or chilling the local injury area.